1. Field of the Invention
The present invention concerns an adapter manifold with dual valve block, and, more specifically, an adapter manifold for the delivery of high purity chemicals having a dual valve block with conduits free of dead pockets.
2. Description of Related Art
Certain manufacturing processes require the delivery of chemicals at high purity levels.
For example, in the semiconductor industry, certain low vapor pressure chemicals, such as tetrakis(dymethilamino) titanium (TDMAT), tetrakis(diethylamino) titanium (TDEAT), tantalum pentaethoxide (TAETO), copper hexafluoroacetylacetonate-trimethylvinylsilane (Cu(hfac)TMVS), tetramethyltetracyclosiloxane (TMCTS), tetraethyl ortosilicate (TEOS), and trimethylphosphate (TMP), are utilized to manufacture semiconductors by a chemical vapor deposition process, which may be in the form of a direct liquid injection (DLI) or of a “bubbler” process.
During the fabrication process, the chemical is stored at a 99.99+% purity level in a first container that has a capacity varying from 100 milliliters to 200 liters and that is known in the art by a variety of common and trade names such as “canister,” “ampoule,” or “host.” From the first container, the chemical is distributed to a second container or to a process tool by a system of manifolds while maintaining the high purity level.
From time to time, it is necessary to replace and clean the first or second containers, for instance, due to maintenance requirements, or to the decomposition of the chemical stored in the container, or for other reasons. Before detaching the container from the manifolds, any remaining chemical must be purged out of the manifolds connected to the container. Typically, the chemical is purged by means of a multi-step process comprising a sequence of blow cycles and of vacuum cycles. Because of the high level of decontamination required, and because some liquid chemical may remain trapped within any dead spaces in the manifolds, this procedure is extremely time consuming, with a consequent negative effect on process yields.
It is desirable to consolidate the valves in the manifolds of these delivery systems into a single valve block, in order in order to minimize the lengths of the connecting tubes, thereby reducing potential areas of entrapment or adhesion of the low vapor pressure chemical. It is also desirable to provide for more compact manifolds, in order to reduce the space requirements of the cabinets where these manifolds and containers are generally located.
U.S. Pat. No. 6,431,229 B1 to Birtcher et al. discloses a purgeable adapter manifold for low vapor pressure chemicals that includes a dual valve block. As shown in FIG. 1, the dual valve block 10 according to the Birtcher invention comprises a first diaphragm valve 12 and a second diaphragm valve 14, having orifices in the seats of the two diaphragm valves that are juxtaposed and connected by a first conduit 16.
A second conduit 18 connects first conduit 16 to the container, therefore connecting the seat sides of both diaphragm valves to the container, while a third conduit 20 connects first conduit 16 to a process tool or to a second container. During ordinary process conditions, both diaphragm valves are in an open condition, enabling the low vapor pressure chemical to flow from second conduit 18 into first conduit 16 and into third conduit 20 and to be delivered to a process tool or to an intermediary container.
During the purge cycle, as a first step, purge gas is blown in a direction opposite to ordinary process conditions flowing from third conduit 20 into second conduit 18. As a second step, second diaphragm valve 14 is closed, and the purge gas flows from third conduit 20 into a fourth conduit 24 and then to a source of vent. As a third step, first diaphragm valve 12 and second diaphragm valve 14 are in a closed condition, and a vacuum purge is performed by applying vacuum at third conduit 20, in order to remove remaining traces of the low vapor pressure chemical.
It will be appreciated that, during the second step of the gas purge, there is no gas flow through a portion of first conduit 16, more specifically, the portion delimited by third conduit 20 at one end and by orifice 26 in the seat of second diaphragm valve 14 at the other end. Therefore, that portion of first conduit 16 constitutes a dead pocket, from which any chemical remaining after the second step of the purge can be removed only by means of a Venturi effect, whereby a pressure differential causes the residual chemical to be drawn from the dead pocket into the stream of the purge gas. In order to accomplish chemical removal through such Venturi effect, however, sufficient time must be allowed for the residual chemical to be drawn out of the dead pocket, causing the purge cycle to be extended. Further, the vacuum purge in the third step must always be performed, to insure that any residual chemical in the dead pocket, not displaced by the Venturi effect, is removed. The length of the vacuum cycle depends on the amount of remaining chemical and on the desired cleanliness level, and requires pumps of adequate capacity with stainless steel components, due to the corrosive properties of the chemical.
Therefore, there is a need for an adapter manifold having a dual valve block that comprises no dead pocket in its conduit system.